{"schemaVersion":1,"slug":"87b-busbar-differential-protection","name":"Busbar differential protection","kind":"function","abbreviation":"87B","aliases":["bus differential","busbar diff","bus zone protection","ANSI 87B","IEEE 87B"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Compares currents at the boundaries of a busbar protection zone.","description":["Compares currents at the boundaries of a busbar protection zone.","The drafting record should connect this function to the CTs bounding the bus zone and any zone-selection status contacts, then trace the bus differential trip matrix and included breakers. Keep the complete designation and equipment tag together so that the SLD, relay logic and terminal schedule describe the same implementation.","The cited mapping is a public manufacturer example (SEL public device-number table). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme."],"readingNotes":["Identify the CTs bounding the bus zone and any zone-selection status contacts.","Trace the bus differential trip matrix and included breakers."],"drawingChecklist":["Label the CTs bounding the bus zone and any zone-selection status contacts.","Cross-reference the bus differential trip matrix and included breakers.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"87B commonly identifies bus differential, but ABB also uses 87B for a phase-B high-impedance element; the application legend resolves the meaning.","facts":[{"label":"Function designation","value":"87B"},{"label":"Base function","value":"87 — Differential protection"},{"label":"Published mapping","value":"SEL public device-number table"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-sel-numbers","relevance":"Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original."},{"sourceId":"ieee-functions","relevance":"Device-number and suffix convention. This page is not a reproduction of the full licensed standard."}],"related":["87-differential","current-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/87b-busbar-differential-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/87b-busbar-differential-protection.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pub-function-sel-numbers","title":"ANSI device-number and suffix reference table","publisher":"Schweitzer Engineering Laboratories","url":"https://selinc.com/pt/products/tables/ansi/","type":"manufacturer","scope":"Public Portuguese-language base-number and application-suffix table. Used to cross-check public number associations. Application-specific and historical labels need the selected drawing legend; this table is not a substitute for the licensed IEEE standard.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original."},{"id":"ieee-functions","title":"IEEE C37.2-2022: power-system device function numbers","publisher":"IEEE","url":"https://ieeexplore.ieee.org/document/9984140","type":"standard","scope":"Device function numbers, acronyms and contact designations. The full publication may require access through IEEE.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Device-number and suffix convention. This page is not a reproduction of the full licensed standard."}]}